1. Totally rework a broken MAJOR current feature:
I'm struggling here; but maybe I'll think of something later!
2. Tweak a broken MINOR current feature:
Resource distribution. Some resources are pretty hard/time consuming to find (gold, etc). IMO most (if not all_ resources should bias towards spawning near cave/surface walls/surfaces. Digging in random directions hoping to find some rare resource isn't fun.
3. Essential MAJOR feature before 1.0:
A core reward loop that keeps players engaged, even in the absence of new content. There's a couple systems there to appeal to different sorts of players. I think the community aspect of the came will keep a fair number of players engaged, but I'm more worried about the folk who lean more towards the RPG side of the game.
There's the loot -> clear a titan -> better loot -> clear a more difficult titan -> even better loot -> etc loop. Though, I think for that to work, we need enough loot tiers to satisfy players for some time, or some randomly generated loot to keep things interesting (diablo- or borderlands style).
Unfortunately, I don't have a concrete feature here, other than a vague worry about keeping people engaged after the first few months of the game releasing.
4. Add a MINOR feature in next update:
The current worlds are pretty hostile to explore for newbies - particularly caves due to high drops, not many openings to the surface, difficult to find caves in some biomes, not enough connections, too wide for a torch to illuminate, etc.
I'd like to propose "cave tiers" to tie into world difficulty. Something along the lines of:
Beginner Worlds: All biomes should have "easy" caves: lightly sloped, not too wide, lots of interconnections, no large drops. A player should be able to find caves in any biome, and should be able to navigate them without much digging, or a grappling hook.
Intermediate Worlds: Some biomes have more unique & hard to traverse caves (canyons, swiss cheese, etc). Larger caves/caverns start to appear. A player should be able to find caves in any biome, but may require some digging/building/grappling to navigate some areas.
Advanced Worlds: Most biomes have difficult to traverse caves. Some biomes caves are hidden; require digging/etc to find them.
FWIW, this is something I'd love to do (yay for the world builder!), but I'm skeptical of my free time.